The process of producing 1,4-butynediol by the continuous aqueous reaction of formaldehyde and acetylene using a copper acetylide complex as a catalyst (commonly called ethynylation), is well known. Such a process is shown, for example, in Kirchner, U.S. Pat. No. 3,650,985. The same process, using a bismuth-modified copper acetylide complex as the catalyst, is shown in U.S. application Ser. No. 794,674, filed May 6, 1977. The U.S. patent and the U.S. application are incorporated into this specification to show these processes.
When the flow of acetylene to such a reaction is interrupted because it is in short supply or because of an accident, and ethynylation stops momentarily, a significant amount of the copper acetylide catalyst is reduced to metallic copper. This metallic copper promotes the formation of cuprene, which clogs filters used in the process and reduces the catalyst's effectiveness.
It has now been found that this cuprene formation can be inhibited and the useful life of the catalyst extended if, when acetylene flow is interrupted, the pH of the reaction mass is reduced from the normal value of 6-8 to a value of about 3.5-5, and is held there until the normal flow of acetylene is resumed.